Nonvolatile memory devices have garnered much interest in recent times, including nonvolatile memory devices made of a phase changeable structure. Referencing FIG. 1, a phase changeable structure typically includes a lower electrode 200 formed in a substrate 100 (e.g., insulating layer), a phase changeable pattern 310 and an upper electrode 410. Aphase changeable pattern can be obtained from etching a phase changeable layer using a mask pattern. The phase changeable pattern is typically located between the lower electrode and the upper electrode and can include a chalcogenide (or calcogenide).
Typically, a predetermined amount of current (e.g., generated by a difference in voltage between the lower electrode and the upper electrode) can be applied to the phase changeable pattern to induce a change in phase from a single crystalline state having a relatively low electric resistance into an amorphous state having a relatively high electric resistance. In addition, if the current applied to the phase changeable pattern is reduced or removed, the phase changeable pattern may be changed from the amorphous state into the single crystalline state.
Generally, after forming a stacked composite of material comprising a phase changeable layer and a conductive material over the phase changeable layer, a first etching process is performed on the conductive material to form an upper electrode. Thereafter, a second etching process is performed on the phase changeable layer to form the phase changeable pattern.
When a conventional etching material (e.g., a chlorine-containing etchant) is used in the first etching process to form the upper electrode, an unacceptable number of defects can be generated at an upper face portion of the phase changeable pattern which contacts the upper electrode. In addition, the use of a conventional etching material (e.g., a chlorine-containing etchant) in the second etching process to form the phase changeable pattern can further contribute to an unacceptable number of defects, e.g., generated at the interface between the phase changeable pattern and the upper electrode and/or at a side face portion of the phase changeable pattern. It is believed that chlorine may reside on a side face of the phase changeable pattern or at an interface between the phase changeable pattern and the upper electrode. It is also believed that this remaining chlorine residue or a byproduct thereof may contribute to defect formation, such as via erosion, in succeeding processes.
An illustration of typical defects, that can be formed, is illustrated in FIG. 1. Defects can occur between the phase changeable pattern 310 and the top electrode 410 as illustrated by reference number 302 in either or both portions of the phase changeable structure. Defects can also occur on a side face of the phase changeable pattern 310, as illustrated by reference numbers 304 and 306. Defects can also occur between phase changeable pattern 310 and the substrate 100 (e.g., insulating layer), as illustrated by reference number 306.